A carbonylation process of olefinically or acetylenically unsaturated hydrocarbon compound with carbon monoxide and hydroxy compound provides a versatile tool for the economic production of various chemicals starting from readily available unsaturated hydrocarbon feedstock. The carbonylation reaction may be represented by the equation: ##EQU1## where A represent the unsaturated hydrocarbon compound and BOH represents the hydroxy compound, such as water (B.dbd.H), alcohols (B.dbd.R), and carboxylic acids (B.dbd.RCO). Generally, olefinic precursors provide saturated products, whereas acetylenic precursors provide olefinic products; multiple carbonylations such as producing saturated products from acetylenic precursors not being excluded. Depending on the nature of the hydroxy compound BOH, various functionalized products, including carboxylic acids, esters, and anhydrides can be obtained.
It has been found that catalytic systems containing cationic palladium, a phosphine ligand, and a protonic acid are well suited for carbonylation reactions. These catalyst systems allow the carbonylation reaction to proceed at high rate under mild conditions in respect of temperature and carbon monoxide pressure. By dedicated choice of the type of phosphine and the nature of the protonic acid, extremely high selectivities to specific desired product could be obtained. For further details of specific carbonylation reactions thus catalyzed reference is made to EP-106379-B, U.S. Pat. No. 4,739,109, U.S. Pat. No. 4,739,110, U.S. Pat. No. 4,940,787, U.S. Pat. No. 4,786,443, U.S. Pat. No. 5,099,062, U.S. Pat. No. 5,158,921, U.S. Pat. No. 5,028,576, U.S. Pat. No. 5,103,043, U.S. Pat. No. 5,158,921, U.S. Pat. No. 5,124,300, U.S. Pat. No. 5,166,411, U.S. Pat. No. 5,166,116, U.S. Pat. No. 5,177,253, U.S. Pat. No. 5,179,225. The low temperatures of these carbonylation reactions are particularly advantageous in that the usual problem of polymerization as side reaction in preparations and/or purifications involving vinylic precursors or products does not occur to an appreciable extent.
Generally, these catalyst systems should comprise a rather high ratio of moles of phosphine to gram atoms of palladium for securing high conversions at low palladium concentration. The high phosphine content disadvantageously attributes to the waste streams and the economics of the above processes, in particularly when using substituted phosphines for specific selective processes. Therefore, it would be desirable to reduce the phosphine/palladium ratio without affecting the performance of these catalyst systems.
The use of inhibitors in other carbonylation reactions and/or preparation processes for methyl methacrylate (MMA) has been reported. However, in such cases the inhibitor was added for its well-known function of inhibiting polymerization reactions of vinylic compounds, since the processes were carried out at temperatures of about 100.degree. C. or much higher. For example, U.S. Pat. No. 4,447,640 discloses the preparation of MMA by carbonylation of 1,2-dihaloalkanes in the presence of a supported palladium catalyst and an inhibitor at temperatures in the range of 150.degree.-300.degree. C. The specification mentions that homogeneous catalysts comprising a group VIII metal salt in conjunction with a triorganic phosphine can also be used, without providing further detail. The alleged effects of inhibitor addition as elucidated in column 4, lines 7-37, are prevention of polymerization of the product and increase of the active life of the catalyst by prevention of fouling of the catalyst through deposit of carbon thereon. The latter problem would clearly seem to be confined to heterogeneous catalysts. U.S. Pat. No. 4,480,116 discloses the preparation of MMA by acid hydrolysis of acetone cyanohydrin in the presence of 50-3000 ppm of specific inhibitors, particularly during the work up procedures. Again, the alleged effect is prevention of polymerization of MMA product, whereas this publication is silent on any effect on the life of the catalyst. In Example 22 of EP-A-386833, the carbonylation of 3-butynol is carried out in the presence of hydroquinone for preventing polymerization of the methylenolactone product formed. U.S. Pat. No. 4,416,823 discloses the dimeric hydroesterification of 1,3-alkadienes in the presence of a palladium/phosphine/thiol stabilized complex catalyst at preferred temperatures in the range of 80.degree.-120.degree. C. Preferably, the reaction is conducted in the presence of a vinyl polymerization inhibitor to avoid an increased incremental loss of 1,3-butadiene to polymeric byproducts. None of these publications give any hint to the reduction of a phosphine/palladium ratio in general carbonylation reactions, let alone the type of carbonylation reaction of the present invention.
It is therefore an object of the present invention to provide a process of carbonylating olefinically or acetylenically unsaturated compounds with carbon monoxide and a hydroxy compound in the presence of a catalyst system comprising a source of cationic palladium, a source of phosphine and a protonic acid with reduced phosphine/palladium ratio.